A: Infrared Absorption 197K.

B: Ultraviolet Absorption 197U—

C: Dissolve 1 g in 10 mL of water, add 10 mL of saturated sodium carbonate solution, and mix. Separate the precipitate by vacuum filtration, using a medium-porosity, sintered-glass filter, and wash with three 5-mL portions of ice-cold water. Dry the crystals at 80 for 1 hour: the phenylpropanolamine so obtained melts between 101 and 104 (see Melting Range or Temperature 741).

Mobile phase— Prepare a filtered and degassed mixture of water, acetonitrile, phosphoric acid, and triethylamine (950:50:8:5). Make adjustments if necessary (see System suitability under Chromatography 621).

System suitability solution— Dissolve suitable quantities of USP Phenylpropanolamine Hydrochloride RS and USP Dextroamphetamine Sulfate RS in water to obtain a solution containing about 5 µg of each per mL.

Amphetamine stock solution— Dissolve an accurately weighed quantity of USP Dextroamphetamine Sulfate RS in water, and dilute quantitatively, and stepwise if necessary, with water to obtain a solution having a known concentration of about 2.5 µg per mL.

Phenylpropanolamine stock solution— Transfer about 2.5 g of Phenylpropanolamine Hydrochloride, accurately weighed, to a 10-mL volumetric flask, dilute with water to volume, and dissolve, using sonication if necessary.

Standard solution— Transfer 4.0 mL of Phenylpropanolamine stock solution, accurately measured, to a 10-mL volumetric flask, add 4.0 mL of Amphetamine stock solution, dilute with water to volume, and mix to obtain a solution having known concentrations of about 100 mg per mL and 1 µg per mL, respectively.

Test solution— Transfer about 4.0 mL of Phenylpropanolamine stock solution, accurately measured, to a 10-mL volumetric flask, dilute with water to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 206-nm detector and a 4.6-mm × 25-cm column that contains 5-µm, base-deactivated packing L1. The flow rate is about 1 mL per minute. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the relative retention times are 1.0 for phenylpropanolamine and 2.1 for amphetamine; the resolution, R, between phenylpropanolamine and amphetamine is not less than 15; and the column efficiency is not less than 10,000 theoretical plates. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the relative standard deviation of the amphetamine peak for replicate injections is not more than 3.0%.

Procedure— Separately inject equal volumes (about 5 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the responses at the locus of the amphetamine peak. Calculate the percentage of amphetamine hydrochloride in the portion of Phenylpropanolamine Hydrochloride taken by the formula: in which 171.67 and 368.49 are the molecular weights of amphetamine hydrochloride and amphetamine sulfate, respectively; CS is the concentration, in µg per mL, of USP Dextroamphetamine Sulfate RS in the Standard solution; CU is the concentration, in mg per mL, of Phenylpropanolamine Hydrochloride in the Test solution; and rU and rS are the peak responses of amphetamine obtained from the Test solution and the Standard solution, respectively: not more than 0.001% is found.